Digital cameras have been widely adopted by both amateur and professional photographers. As resolution of digital cameras increases, and the cost of non-volatile memory cards decreases, more photographers are moving from film to electronic imaging.
The resolution of many current digital cameras ranges from 2.1 megapixels (MP) to 4.2 MP. Cameras with higher resolution are available but are typically used by advanced amateurs or professionals. A 2.1 MP camera captures an image as an array of 1600 (horizontal) by 1200 (vertical) pixels; a 4.2 MP camera has an image sensor with a 2272×1704 array of pixels. Images from a 2.1 MP camera can be typically enlarged to 5×7 inch prints with good results; 3.3 MP and 4.2 MP cameras yield very satisfactory prints to 8×10 inches.
Data from the image sensor is typically compressed using joint photographic experts group (JPEG) processing to decrease the size of the image file, and the file is then stored on a non-volatile memory card in the camera. Image files can then be downloaded to a computer, emailed to others, modified to enhance the image, and printed on low-cost consumer printers.
One use of a digital camera is to capture images of documents. Many digital cameras have auto focus capability allowing accurate focus on, for example, an 8.5×11 inch document. Given adequate lighting, an image of the page can be obtained. However, the limited resolution of the camera limits imaging of small text or detail in document illustrations. If the 11-inch dimension of a document is aligned with the larger (horizontal) imaging axis, a 4.2 MP image sensor provides 2272 pixels/11 inches, or 206 pixels per inch of document. Many document scanners use at least 300 pixels per inch (more commonly referred to as “dots per inch” or DPI). Even a 4.2 MP camera falls considerably short of this level. More common 2.1 MP or 3.3 MP cameras provide even less resolution.
Linear scanners capable of 300 DPI and higher are widely used in flatbed scanners and facsimile machines. The document to be scanned is either moved past the linear scanner (typical in facsimile machines) or the scanner is moved past the document (typical in flatbed scanners). Portable scanners have been developed which are manually moved across a document to be scanned, in one or more passes depending on the scanner width and size of the document. These portable scanners typically have internal memory for storing the images scanned, which can later be transferred to a PC.